1. Field of the Invention
The present invention relates to an ultrasonic security system for personal computer by means of using a touch-panel section, a lock section, and a key section.
2. Description of the Prior Art
Construction of a security system for personal computer (PC) such as wearable PC, desktop- and laptop PCs, and notebook PC prevents the influence of noises and invaders, and makes it difficult to steal information through the PC, and in addition keeps a communication secret. However, it is difficult to keep secret by using the coding technique based on conventional hardware such as magnetic cards and IC cards. The magnetic cards are very convenient and popular, however it is easy to make copies thereof or steal passwords. The IC cards are superior to the magnetic cards in difficulty in counterfeiting of cards, however it is not enough to keep the information secret thoroughly.
Recently, touch panels in place of keyboards are convenient, especially for wearable PC. Conventional touch panels with, for example, ultrasonic transducers such as a wedge-shaped transducer and a piezoelectric thin film transducer make use of disappearing of an output electric signal, which disappears in response to a disappearance of an ultrasound on a touch panel by touching thereon. Disappearing of the output electric signal makes signal analysis complicated, and makes it difficult for the conventional touch panels to be of use as hardware for the coding technique.
An object of the present invention is to provide an ultrasonic security system for personal computer having a touch-panel section, which is contributory to the coding technique.
Another object of the present invention is to provide an ultrasonic security system for personal computer preventing the influence of noises and invaders.
Another object of the present invention is to provide an ultrasonic security system for personal computer making it difficult to steal information.
Another object of the present invention is to provide an ultrasonic security system for personal computer keeping a communication secret.
Another object of the present invention is to provide an ultrasonic security system for personal computer excellent in manufacturing and mass production.
Another object of the present invention is to provide an ultrasonic security system for personal computer operating under low electric power consumption with low voltage.
A still other object of the present invention is to provide an ultrasonic security system for personal computer having a small-sized circuit with a simple structure which is very light in weight.
According to one aspect of the present invention there is provided an ultrasonic security system for personal computer comprising a touch-panel section, a lock section, and a key section. The touch-panel section comprises a nonpiezoelectric plate, at least one transducer-unit, and a signal analyzer. The lock section comprises a second piezoelectric substrate, a coding interdigital transducer (IDT) consisting of interdigital electrode pairs and having a coded pattern, and a terminal IDT having the electrode-finger direction parallel to that of the coding IDT. The key section comprises a third piezoelectric substrate, an initial IDT, and a decoding IDT having the same construction pattern as the coding IDT. The transducer-unit consists of at least one input IDT Ti (i=1, 2, . . . , m), at least one output IDT Ri (i=1, 2, . . . , m), a first input piezoelectric substrate, and a first output piezoelectric substrate. The input IDT Ti has an interdigital periodicity P and an overlap length L. The output IDT Ri has the electrode-finger direction slanting to that of the input IDT Ti by an angle xcex8, and has an interdigital periodicity PN along the orthogonal direction to the electrode-finger direction of the output IDT Ri and an overlap length LP along the electrode-finger direction of the output IDT Ri.
When an input electric signal is applied to the input IDT Ti, a first surface acoustic wave (SAW) is excited in the first input piezoelectric substrate. The first SAW is transmitted to the first output piezoelectric substrate along an upper end surface of the nonpiezoelectric plate, and transduced to electric signals Ej (j=1, 2, . . . , n) at the output IDT Ri. Thus, SAW propagation lanes Wj (j=1, 2, . . . , n) on the upper end surface of the nonpiezoelectric plate are formed between the input IDT Ti and the output IDT Ri. In this time, the phase delays of the electric signals Ej linearly correlate to the SAW propagation lanes Wj. If touching one of the SAW propagation lanes Wj, one of the electric signals EJ is detected at the output IDT Ri. The one of the electric signals EJ is applied to the coding IDT, so that a second SAW based on the coded pattern is excited on the second piezoelectric substrate. The second SAW is detected as a coded burst-signal at the terminal IDT. The coded burst signal arrives at the initial IDT, so that a third SAW is excited on the third piezoelectric substrate. In this time, if the third SAW correlates to the coded pattern, a pulse is detected at the decoding IDT. The pulse arrives at the signal analyzer. As a result, the one of the SAW propagation lanes Wj is sensed by means of the phase of the pulse.
According to another aspect of the present invention there is provided at least one output IDT Ri having the interdigital periodicity PN which is equal to the product of the interdigital periodicity P and cos xcex8, and the overlap length LP which is equal to not only the product of the overlap length L and sec xcex8, but also the product of the interdigital periodicity P and cosec xcex8.
According to another aspect of the present invention there are provided first input-, first output-, second-, and third piezoelectric substrates made of a piezoelectric ceramic, respectively, the polarization axis thereof being parallel to the thickness direction thereof.
According to another aspect of the present invention there are provided first input-, first output-, second-, and third piezoelectric substrates having a thickness smaller than the interdigital periodicity P, and a nonpiezoelectric plate having a thickness larger than three times the interdigital periodicity P.
According to another aspect of the present invention there is provided an ultrasonic security system for personal computer, wherein the phase velocity of the first SAW on the nonpiezoelectric plate alone is higher than that in the first input-, and first output piezoelectric substrates alone.
According to other aspect of the present invention there is provided an amplifier connected between the signal analyzer and the input IDT Ti.
According to a further aspect of the present invention there is provided an ultrasonic security system for personal computer comprising a touch-panel section, a lock section, and a key section. The touch-panel section comprises a nonpiezoelectric plate, two transducer-units, and a signal analyzer. The lock section comprises a second piezoelectric substrate, two coding IDTs, and two terminal IDTs. It is possible for the coding IDTs to have the different coded patterns from each other. The key section comprises a third piezoelectric substrate, two initial IDTs, and two decoding IDTs.
When an input electric signal is applied to the input IDT Ti of each of the transducer-units, a first SAW is excited in the first input piezoelectric substrate. The first SAW is transmitted to the first output piezoelectric substrate along an upper end surface of the nonpiezoelectric plate, and transduced to electric signals Ej (j=1, 2 . . . , n) at the output IDT Ri of each of the transducer-units. Thus, SAW propagation lanes Wj (j=1, 2, . . . , n) on the upper end surface of the nonpiezoelectric plate are formed between the input IDT Ti and the output IDT Ri. If touching one of the SAW propagation lanes Wj, one of the electric signals Ej is detected at the output IDT Ri. The one of the electric signals Ej is applied to each of the coding IDTs, so that a second SAW based on the coded pattern is excited on the second piezoelectric substrate. The second SAW is detected as a coded burst-signal at each of the terminal IDTs. The coded burst signal arrives at each of the initial IDTs, so that a third SAW is excited on the third piezoelectric substrate. In this time, if the third SAW correlates to the coded pattern, a pulse is detected at each of the decoding IDTs. The pulse arrives at the signal analyzer. As a result, the one of the SAW propagation lanes Wj is sensed by means of the phase of the pulse.